A. Field of the Invention
The invention generally concerns a process for making pyrochlores, such as those that can be used as catalysts in chemical reactions.
B. Description of Related Art
Traditionally, pyrochlores have been synthesized by the so-called “Pechini” method (See, U.S. Pat. No. 3,330,697; and Sarthak Gaura et al. in “Rh, Ni, and Ca substituted pyrochlore catalysts for dry reforming of methane”, Applied Catalysis A: General 403 (2011) 142-151; Devendra et al., in “Role of metal substitution in lanthanum zircon ate pyrochlores (La2Zr2O7) for dry (CO2) reforming of methane (DRM)”. Appl. Petrochem. Res. (2012) 2:27-35). In general, the Pechini method is based on a blending of positive ions in a solution, controlled transformation of the solution into a polymer gel, removal of the polymer matrix and development of an oxide precursor with a high degree of homogeneity. During the Pechini process, metal salts or alkoxides are introduced into a citric acid solution with ethylene glycol. The solution is heated to over 400° C. Polycondensation of ethylene glycol and citric acid starts above 100° C., resulting in polymer citrate gel formation. When the heating temperature exceeds 400° C., oxidation and pyrolysis of the polymer matrix begin, which lead to the formation of X-ray amorphous oxide and/or carbonate precursor.
The primary problems with the Pechini method are that it is labor intensive and not cost effective. Moreover, the current methods that are available to attach the catalyst on a support material are also inefficient. Such methods oftentimes result in the production of a supported catalyst that lacks a sufficient amount of catalytic surface area while also failing to create a strong support-metal interaction to maximum activity and reduce sintering during their usage.
While proposed modifications to the Pechini method have been made, such modifications suffer from the same problems noted above. For instance, co-precipitation methods such as those disclosed in U.S. Pat. No. 8,241,600, add costs and complexity to the process.